The most abundant biomass material on earth is cellulose, a polysaccharide. It is a major component of plant cell walls. Exploitation of cellulose is vital to provide a renewable source of fuels and chemical feedstocks as oil reserves begin to diminish. Cellulases are a class of enzymes that degrade cellulose to oligosaccharides and glucose. We have obtained crystals of a bacterial cellulase from an extremely alkylophilic species of Bacillus. It diffracts to at least 1.8 E resolution at room temperature, using a rotating anode x-ray source. We have prepared a HgI3 derivative, which also diffracts to high resolution, and can locate the heavy-atom sites from inspection of difference Patterson maps. We need access to synchrotron facilities in order to conduct a MAD phasing experiment, using the Hg atom as the anomalous scattering site, and to obtain very high resolution data.